The present invention relates to interferometers of the Fabry-Perot type and more particularly to an improved reflective Fabry-Perot interferometer.
The Fabry-Perot interferometer is a multiple-beam interferometer normally consisting of two parallel plates of glass or quartz capable of light refraction separated a short-known distance and with the adjacent surfaces partially silvered so as to increase reflection without being fully opaque. This instrument is capable of very high resolution of two very close spectral lines.
The Fabry-Perot resonant cavity can also be used as a narrow wavelength band rejection element when used in the reflective mode.
The use of a non-moving element to cover the transitions associated with the wavelength region of interest may require a wider plate separation than normally employed in a movable mirror interferometer. Such an arrangement leads to a loss of portions of successive reflections in the resonant Fabry-Perot cavity through the edge of the cavity adjacent the ends of the two mirrors. The reason for this loss of light at the edge of the cavity is that the mirrors extend only a finite distance. This spoils the coherent multiple reflections necessary to create the extinction of unwanted wavelengths, in the reflective mode, at angles other than normal incidence.